Thermostatic apparatus



Jan. 20, 1942. E. N. LIGHTFOOT THERMOSTATIC APPARATUS Filed Feb. 13,1939 I'I'IIII n -x wi llllll WWW 495mm fill Patented Jan. 20, 1942THERMOSTATIC APPARATUS Edwin N. Lightfoot, Wauwatosa, Wis., assignor toCutler-Hammer, Inc., Milwaukee, Wis., a corporation of DelawareApplication February 15, 1939, SerialNo. 256,240

8Clainis. (01.200-137) This invention relates to thermostatic apparatusand while not limited thereto it is particularly applicable tothermostatically operated electric switches.

An object of the invention is to provide an improved thermostaticoperating mechanism which is simple in construction and easily assembledand maintained.

Another object is to provide a mechanism which may be adjusted tooperate between very close limits of temperature variations, while beingat the same time adjustable at will for operating ranges from very lowto very high average temperatures.

Another object is to provide a mechanism 1 which is not overstrained ifit is subjected to a temperature which greatly departs from theoperating limits for which it is adjusted.

- Another object is to provide a thermostat the operation of which isindependent of the position in which'it is mounted.

Thermostatic apparatus in accordance with the present invention providesfor a pivoted actuator or lever which is supported for limited rotarymovement in two spaced open pivotal 2 bearings-each comprisingcooperating elements,

one of the bearings having one element thereof provided on the lever andthe other on a base, while one element of the other bearing is alsoprovided on the lever and the cooperating element on one end of athermally responsive rod the other end of which is attached to the base.The two elements of both bearings are biased into respective, engagementby a spring acting on the lever whose rotary motion may be limited ineither direction in any suitable manner. If the rod expands or contractsbeyond the limit corresponding to the rotation of the lever in one orthe other direction, the elements of the respective bearing separate andthus prevent undue strain on the lever or the parts connected thereto.

Thus by providing for a limitation of the retary movement of theactuator about an open pivotal bearing, the pivot and cooperatingbearing surface of the hearing are separated from 7 each other by arelative radial movement when the limit. of rotation about such bearingis reached, that is when the device is subjected to temperatures outsideof the range of its adjustl0 ment, This prevents excess rotary motionfrom being transmitted to the delicate parts of the device andoverstraining' of the parts. Other objects and advantages willhereinafter I forms with a sheet metal cover 2 a housing for an electricswitch 3, which may be of any of a number of types of snap switches, butis preferably of a type requiring a minimum of movement and operatingforce and closing and openingits contacts with a snap action. The switchshown has its contacts totally enclosed in an insulating casing and isprovided with a reciprocable operating rod 4 which projects outside ofsaid casing. The switch casing is mounted on the frame I.

A tube 5 of. a material which expands and contracts with changes intemperature has its one end threaded into a boss 6 of the frame I, whileits outer end is closed by a plug 1 which is soldered-or otherwisefastened in the end of the tube. The tube 5 may be screwed into the basea greater or lesser distance to adjust its length and it is locked inthe proper position by a lock nut 8. Inside of the tube 5 is arranged asecond tube 9 of a temperature expansible material having a temperaturecharacteristic differing from that of the tube 5, so that upon changesin ambient temperature the two tubes expand and contract by differentamounts. The tube 9 haspreferably a very low coeflicient of expansionwhich is negligible in relation to that of tube 5. The lowerend of thetube 9 is provided with an abutment .10 which has a reduced shank II.and which is guided in the tube 9 to hold the abutment lfl tightly tothe rod 9. The upper end of the tube 9 is equipp d with an operating pinI! which transmits the thrust of the tube 9 and which for that purposeis provided with a shoulder l3, abutting the end of tube I while itsouter end is a cone it which protrudes into the housing through a holeis.

Inside of the base, adjacent to the hole I! are 6 ings. The respectivebearing elements are kept in engagement with each other by a helicalload spring l8, which is provided with cups [9 and 20 at its respectiveends. Mounted centrally of the cup I! is a point 2| which engages arecess on the inner surface of the lever ll opposite of the bearings andabove and within the area bounded by the three points l4 and IS. The cup20 is provided with a central indentation to receive a point 22 which ismounted on a lug 23 which forms part of the frame I.

The load spring is compressed to apply a pressure upon the bearingsthereby maintaining the tube 8 in compression, while at the same time ittends to rotate the lever ll counterclockwise as depicted in Fig. 1, asthe lever fulcrums about the points I6.

The upper ends of the lever ll are bridged by a block 24 which isriveted to the lever. A screw 25 is threaded into the block 24 at apoint opposite to the operating rod 4 so that one end of the screwnormally bears against the rod. The other end of the screw has a knurledhead to facilitate manual adjustment thereof. A spring 26 which is heldin compression between the block 24 and the knurled head of the screw 25is wound about the screw to increase the frictional engagement of thescrew and prevent the latter from turning and thereby change itsadjustment. Another compression spring 21 may be interposed between thelever I1 and the frame I to amplify the bias of the spring H, but thespring 21 may also be omitted. Furthermore, the spring 21 may bearranged to transmit its pressure to the frame I through a screw 28,fastened to the frame I and provided with a thread which engages a nut29. By turning the nut the compression of the spring 21 may be varied tothereby vary the bias of the lever ll.

The tube 5 is preferably the element having a high coefficient ofexpansion, while the tube 9 should have a low or zero coeflicient ofexpansion and is preferably made of quartz. The tube 0 maybe replaced bya solid rod, and it is also possible to arrange the elements 5 and 9 inparallel arrangement side by side in place of the concentric arrangementshown. The device may be employed to respond to temperature changes ofgaseous or liquid media and by suitable changes of the temperatureresponsive elements it may be used to respond to the temperaturevariations of a solid object.

In operating the device it is so adjusted that for the minimum desiredtemperature the lever l1 permits the operating rod 4 to occupy itsoutermost position. If now the temperature increases the element 5expands more than the element 9. This causes the lever H to rotatecounterclockwise until the screw 25 pushes the rod 4 sufficientlyinwardly to operate the switch 3. Thereafter decreased temperature willcause shortening of tube 5 and clockwise rotation of the lever l'l untiltheswitch 3 is again operated in the reverse direction. If the devicewhile adjusted to operate in a very high temperature range should beexposed to very low temperature, the lever continues to rotate clockwiseuntil ultimately its rotation is stopped. Thereafter the lever is liftedoff the points l8, while the spring II is further compressed without anyundue strains being exerted on 'the operating parts. If the temperaturerises again the lever ultimately again engages the pivots I6. It willalso be noted that if the device is adjusted for a low averagetemperature and this is greatly reduced, the pin It leaves the lever IIwhich then remains at rest on the pivots IE to be engaged again by thepin l2 upon a rise in temperature to within the adjusted range. Thus themechanism is protected at all times from excessive stresses and isalways ready to operate at its adjusted temperature level after havingbeen exposed to temperatures far outside of said level.

It is obvious that the relation of the parts may be reversed so that thelever I I rotates in a direction opposite to that described forcorresponding temperature changes.

It is obvious that the points of bearings l5 and the cone bearing [4 mayalso be replaced by a knife edge or other type of abutment providingopen pivotal bearings.

What I claim as new and desire to secure by Letters Patent is:

1. In a thermostatic switch the combination of a base, an electricswitch mounted on said base and having an actuator to operate theswitch, a lever for operating said actuator, an adjustable abutment forsaid actuator on said lever, two suporting points on said base, twoparallel thermoresponsive rods having different temperature coefficientsof expansion and having one of their respective ends joined together,the other end of one of said rods being adjustably attached to saidbase, a third supporting point at the other end of said other rod, saidsupporting points being arranged in a triangle whose plane issubstantially normal to said rods, a lever having bearing surfaces forsaid points, each of the surfaces forming with the respective point anopen pivotal bearing, and a spring between said base and said lever andapplying to the latter a biasing force in a direction substantiallyparallel with said rods and passing through said triangle to bias saidlever toward said points.

2. In a thermostatic mechanism, the combination of a base, a lever, anopen pivotal bearing interposed between said base and one end face ofsaid lever, a thermoresponsive rod having its one end fastened to saidbase, a second open pivotal bearing interposed between said end face ofthe lever and the other end of said rod, and a spring bearing againstthe opposite face of said end of the lever and arranged to normally biasthe elements of the respective bearings into engagement with each otherand to afford rotation of said lever about said bearings simultaneously.

3. In a thermostatic mechanism, the combination of a base, a lever, anopen pivotal bearing having cooperating bearing surfaces on said baseand one end face of said lever, a thermoresponsive rod having its oneend adjustably fastened to said base, another open pivotal bearinghaving cooperating bearing surfaces on said rod and said end face of thelever, and a spring interposed between said base and theopposite face ofsaid end of the lever to normally maintain the cooperating surfaces ofthe respective bearings in contact with each other and to aifordrotation of said lever about said several bearings simultaneously.

4. In a thermostatic mechanism, the combination of a base, a lever, anopen pivotal bearing having cooperating bearing surfaces on said baseand one end face of said lever respectively, two parallelthermoresponsive rods having different temperature coefficients ofexpansion and having one pair of their respective ends joined together,the other end of one of said rods being adjustably attached to andpositively locked in adjusted position relatively to said base. motheropen pivotal bearing having cooperating bearing surfaces on the otherend of said other rod and on said end face of the lever, and a springinterposed between said base and the opposite face of said end of thelever to normally maintain the cooperating surfaces of the respectivebearings in contact with each other and to afford rotation of said leverabout said several bearings simultaneously.

5. In a thermostatic mechanism, the combination of a base, a lever, anopen pivotal bearing having cooperating bearing surfaces on said baseand on one end face of said lever, a thermoresponsive rod having its oneend fastened to said base, another open pivotal bearing havingcooperating bearing surfaces on said rod and said end face of the leverto cause the latter to rotate about said first bearing in response totemperature changes of said rod, and a spring interposed between saidbase and the opposite face of said end of the lever to normally maintainthe cooperating surfaces of the respective hearings in contact with eachother and to afford rotation of said lever about said several bearingssimultaneously.

6. In a thermostatic mechanism, the combination of a base provided withan abutment, a thermoresponsive rodhaving one end attached to said baseand its other end provided with another abutment spaced laterally fromsaid former abutment, a lever provided with bearing surfaces on one endface thereof for engaging said abutments, each of said bearing surfacesforming with the respective abutment an open pivotal bearing forrotational movement of the lever thereabout, and a spring at theopposite face of said end of the lever normally maintaining saidsurfaces in engagement with the respective abutments and affordingrotation of said lever about said several bearings simultaneously, whilepermitting separation of the bearing surface and abutment of one of thebearings upon changes in temperature of said rod beyond a given limit.

7. In a thermostatic switch the combination of a base, an electricswitch complete in itself mounted on said base and having an actuator tooperate the switch, a lever for operating said actuator, an open pivotalbearing having cooperating bearing surfaces on said base and on one endface of said lever, a thermoresponsive rod having its one end fastenedto said base, another open pivotal bearing having cooperating bearingsurfaces on said rod and said end face of the lever, and a springinterposed between said base and the opposite face of said end of thelever to maintain the cooperating surfaces of the respective bearings incontact with each other and to afford rotation of said lever about saidseveral bearings simultaneously.

a. In a thermostatic switch the combination of a base, an electricswitch complete in itself mounted on said base and having an actuator tooperate the switch, a lever for operating said aotuato an open pivotalbearing having cooperat g bearing surfaces on said base and on one endface of said lever respectively, two substantially parallelthermoresponsive rods having different temperature coefficients ofexpansion and having one of their respective ends joined together, theother end of one of said rods being adju'stably attached to andpositively locked in adjusted position relatively to said base, anotheropen pivotal bearing having cooperating bearing surfaces on said otherend of said other rod and on said end face of the lever, and a springin-

